Conventional printed circuit (PC) boards used in high-speed digital systems (e.g., mother boards used for high-speed computers) consist of fiberglass-epoxy resin insulating layers supporting bonded and/or socketed integrated circuits (IC's) and have metallic traces (e.g., copper) that provide power, ground and signal lines. The speed of microprocessors and related computing chips has been increasing at an exponential rate, validating Moore's law, which predicts a doubling of data rates every 18 months.
It is predicted that in approximately five years, the speed demands on copper transmission lines on PCBs will reach their ultimate bandwidth limit of approximately 50 gigabits per second (Gb/s). This limit is imposed by the combination of signal attenuation and frequency dispersion. Even today, these effects are driving PC board designers away from bit-parallel, multi-drop busses towards bit-serial point-to-point connections. In addition, as signaling speeds increase, and operating voltage levels drop, conventional PC board transmission lines are becoming a major source of electromagnetic radiation and cross-talk, which limits the density (pitch) of interconnections and, ultimately, the number of gigabits of I/O per second per inch of chip periphery (Gb/sec/in).
The foregoing considerations are driving circuit and systems designers towards optical interconnects. However, optical interconnect systems may add a significant cost to the fabrication of a PC motherboard. Other, even more exotic approaches are being investigated, including photonic crystal waveguides and imbedded millimeter waveguides. However, these approaches are unproven and also likely to add significant costs.